THE PROBLEM OP MITOSIS. 
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science, and its acceptance necessitates the assumption that 
in the unirerse two sets of physical principles exist, diametri- 
cally opposed to one another. Which of these alternatives 
does Hartog ask us to accept ? He asks us to accept the 
first ; for he says that the visible structures of the polar stars 
and spindle are “ material chains of force of more permeable 
substance than the rest of the field, held in position by the 
stresses radiating from the unlike poles.” But this alterna- 
tive has been shown to imply the inconceivable ; and, since 
an explanation implies something that can be conceived, the 
assumption of his new force cannot explain spindle formation. 
We must now ask if this new force can be the cause of the 
mitotic processes that result in the separation of daughter- 
bodies into two groups. We find that it cannot cause the 
divergence of either the centrosomes in the prophase, or the 
daughter-chromosomes in the anaphase. In the case of the 
former the unlike signs postulated must entail attraction and 
not repulsion : and Hartog himself has realised this ; for in 
order to explain centrosome divergence he has been forced to 
assume “a bodily pull exercised by the cytoplasm.”^ In the 
case of the latter the daughter-chi’omosomes must presumably 
become inducted more strongly by the near than by the 
farther pole, and since the presence of unlike charges can 
cause only attraction, other forces must again be invoked to 
explain this divergence. But if essential processes of mitosis 
cannot be explained without invoking forces to counteract 
the effect of the new mitokiuetic force, how can this latter 
force be put forward as the cause of mitotic phenomena ? It 
cannot be so put forward. And, since the new force postu- 
lated by Hartog can neither cause the formation of the 
spindle, nor effect the processes for which mitosis has been 
instituted, his entire theory is found to be inadequate. 
Before, however, leaving the subject let us look again into 
* Since writing this I have received a communication from Prof. 
Hartog, who says that he now believes that centrosome divergence is 
caused by like osmotic and electric charges, which counteract the 
heteropolar mitokinetic force. 
